I haven't played Mumu all weekend. Why? I'm too busy identifying faces in my digital photos with Picasa.
It's addictive. First Picasa looked at all the photos on my hard drive. Then it spotted most of the faces. Then I told it who some of the faces were. Then it started guessing at matching faces. That's when it became obsessive.
There's a quick intro to Picasa 3.6 and its face recognition at MakeUseof.